It is generally understood to be both economically and environmentally desirable to minimize the amount of raw material contained in thermoplastic spun filaments that make up a variety of fabrics. Generally speaking, less raw material results in lower basis weight webs that cost less and conserve resources.
One problem associated with many conventional woven and nonwoven fabrics is that it is difficult to maximize the ability of a fabric to cover or serve as a barrier or shield while maintaining desirable breathability or permeability. For example, it is desirable for gases and/or vapors (e.g., water vapor) to pass freely or diffuse through a fabric even though the same fabric functions to substantially bar or shield liquids (e.g., liquid droplets) and/or electromagnetic radiation (e.g., visible or ultraviolet light) from an object covered by the fabric.
An equally significant problem is that many fabrics made from spun filaments and/or fibers have unsatisfactory tactile properties. As an example, fabrics containing substantial amounts of filaments and/or fibers that are conventionally melt-spun from economical, recyclable polymers such as, for example, polypropylene, polyethylene and the like, often can have smooth, untextured surfaces and/or relatively large diameters. These filaments and/or fibers can have a "waxy" or slick feel that may be perceived as undesirable. Many applications of such fabrics are thwarted by their inability to be perceived as relatively "cloth-like" (e.g., not slick or "waxy" in a tactile sense).
Fabrics made of filaments and/or fibers composed of a single material or blends of materials (e.g., substantially mono-component filaments and/or fibers) have been subjected to hot calendaring to improve the fabrics' covering or barrier properties. Unfortunately, the resulting fabrics have been characterized as "paper-like" (i.e., stiff and "noisy" or producing sounds when flexed). Such fabrics have exhibited poor drape, flexibility and even breathability. This is generally attributed to individual components of the fabric (e.g., filaments and/or fibers) melting, bonding and/or fusing together during the hot calendaring operation.
Attempts have been made to reduce the slick or "waxy" feel of some filaments and/or fibers by incorporating an expanding agent into the entire filament/fiber or into the sheath of a sheath-and-core conjugate filament and/or fiber. Such materials have been converted into fabrics intended to have "cloth-like" tactile properties. However, these materials fail to address the important problems of reducing the basis weights of the webs and improving the covering or shielding ability of the fabrics.
While these attempts may be of interest to those engaged in the manufacture of fabrics and/or filament (i.e., filaments and/or fibers) they do not address the need to minimize the amount of raw material contained in thermoplastic spun filaments that make up a variety of fabrics while achieving a satisfactory level of fabric softness, drape and flexibility.
For example, there is a need for a fabric that can be manufactured from an inexpensive raw material (e.g., polypropylene, polyethylene and the like) than can satisfy these requirements. A need also exists for a fabric that minimizes the amount of raw material contained in fabric while achieving a satisfactory level of fabric softness, drape and flexibility as well as an acceptable level of cover and/or shielding from liquids and/or electromagnetic radiation (e.g., visible and ultraviolet light). Additionally, a need exists for a fabric formed from an relatively inexpensive raw material that meets these requirements and also has "cloth-like" tactile properties and/or which provides acceptable levels of permeability or breathability. Furthermore, there is a need for a practical process for producing such a material that is relatively simple and can be adapted to modern high-speed manufacturing processes.
Meeting these needs is important since it is both economically and environmentally desirable to reduce the amount of raw material used in fabrics and/or filaments/fibers and still provide a fabric having enhanced covering, barrier and/or shielding properties. It is also both economically and environmentally desirable to produce such a fabric while also providing satisfactory levels of permeability, breathability, flexibility and/or drape.